Cairo Dock 3.0 has been released recently, getting GTK3 support and many enhancements:

A new Twitter applet lets you tweet in one click

A new applet to inhibit the screensaver

Cairo Dock now uses GTK3

The Log out applet has been rewritten, now allowing you to switch users

Much better keyboard support: you can activate a launcher by pressing a shortkey and its number (like in Unity) and also, there are many new keyboard shortcuts

Enhanced taskbar

The Ubuntu Sound Menu has been integrated into the Sound-Control applet

Separators are transparent to click in 'Panel' mode

Text drawing (e.g. with Clock) has been improved

The new default theme with a panel is now included in the core package

Starting with version 2.4.0, Cairo Dock comes with its custom GNOME Session so you can use it as a stand-alone "shell". In version 3.0, a new session has been added which lets you use Cairo Dock with the Unity 2D top panel:

Here are a few more screenshots and a video with the latest Cairo Dock 3.0 in action: